Drill string joint breaking means

ABSTRACT

A rock drill has a chuck which is arranged to be displaced along a feed bar by means of a feed motor. The chuck is of the kind which is hydraulically actuated and grips the drill pipe when pressurized and it is rotated by means of a reversible hydraulic motor having two alternative supply conduits. The chuck is connected to the supply conduit for providing reverse rotation by means of a conduit in which a delaying valve is arranged. Thus, when the supply conduit for providing reverse rotation is pressurized upon actuation of a manually operated valve, the drill pipe being firmly held by a drill pipe holder, the delaying valve delays the supply of hydraulic fluid to the chuck until the hydraulic rotation motor and thereby the chuck has started its backward rotation so that the kinetic energy of the chuck and the motor is utilized for breaking a drill string joint located between the holder and the chuck.

United States Patent Jonsson 1 Oct. 10,1972

[54] DRILL STRING JOINT BREAKING MEANS [73] Assignee: Atlas CopcoAktiebolag,

Sweden [22] Filed: May 28,1971

[21] Appl.No.: 147,988

Nacka,

[30] Foreign Application Priority Data June 15, 1970 Sweden ..8254/70[52] US. Cl. ..173/149, 8l/57.l9, 173/164, 279/4 [51] Int. Cl ..E21cl/l0 [58] Field of Search.....173/l64, 152; 175/85; 279/4; 81/57.]9;166/725, 315; 192/.096

Primary Examiner-Emest R. Purser Attorney-Munson & Fiddler ABSTRACT Arock drill has a chuck which is arranged to be displaced along a feedbar by means of a feed motor. The chuck is of the kind which ishydraulically actuated and grips the drill pipe when pressurized and itis rotated by means of a reversible hydraulic motor having twoalternative supply conduits. The chuck is connected to the supplyconduit for providing reverse rotation by means of a conduit in which adelaying valve is arranged. Thus, when the supply conduit for providingreverse rotation is pressurized upon actuation of a manually operatedvalve, the drill pipe being firmly held by a drill pipe holder, thedelaying valve delays the supply of hydraulic fluid to the chuck untilthe hydraulic rotation motor and thereby the chuck has started itsbackward rotation so that the kinetic energy of the chuck and the motoris utilized for breaking a drill string joint located between the holder12 Claims, 9 Drawing Figures [56] References Cited UNITED STATES PATENTSand the Chuck- 3,021,739 2/1962 Grundmann ..81/57.19

in o

PATENTEDUCT 10 m2 sum 1 or 5 I NILS GUNNAR JONSSON I NVE NTOR.

BY MUNSON & FIDDLER PATENTEDnm 10 I972 3.696, 8 72 sum 2 or 5 Fig.4

U U NILS GUNNAR JONSSON INVENTOR.

BY MUNSON & FIDDLER PATENTEDncno m2 3.696.872

SHEET 3 OF 5 I1 000 000 Kg mm H|I[l INVENTOR.

48 NILS GUNNAR JONSSON MUNSON & FIDDLER PKTE'N'TEBnm 10 m2 SHEET UF 5INVENTOR.

NILS GUNNAR JONSSON MUNSON & FIDDLER DRILL STRING JOINT BREAKING MEANSThis invention relates to a drill string joint breaking means which isused in connection with a rock or earth drilling apparatus and comprisesa drill string holder and a power rotated chuck in axial alignment whichare arranged for gripping the drill string and breaking a drill stringjoint located between the holder and the chuck. More specifically, thechuck is the chuck which is used also during drilling for rotating andfeeding the drill string.

In rock drilling, the joints of the drill string will sometimes becomeso tight during drilling that the rotation motor is not capable ofbreaking the joints and it is therefore an object of the invention toprovide for a reliable breaking of the drill string joints.

The above and other objects of the invention are obvious from thefollowing description and from the accompanying drawings in which rockdrilling apparatus including drill string joint breaking means inaccordance with the invention is described by way of example.

In the drawings, FIG. 1 is a side view, partly in section, of the rockdrilling apparatus arranged for vertical drilling; FIG. 2 is a frontelevation partly in section, of the drilling apparatus illustrated inFIG. 1; FIG. 3 is an enlarged section on line 3-3 in FIG. 1; FIG. 4 isan enlarged section of line 44 in the FIGS. 1 and 5; FIG. 5 is anenlarged section substantially on line 55 in FIG. 1, a chuck beingillustrated in a section taken along line 5-5 in FIG. 4; FIG. 6 is adiagram of the pressure fluid system of the drilling apparatusillustrated in the FIGS. l-S; FIG. 7 is a longitudinal section through avalve which is indicated in FIG. 6', and FIGS. 8 and 9 are longitudinalsections through modified embodiments of the valve shown in FIG. 7.

In the various figures, corresponding details have been given the samereference numeral.

The drilling apparatus illustrated in FIGS. 1-5 has a feed bar 11 whichis supported by expanding units 12. Alternatively the feed bar may becarried by a wheeled substructure or be supported in another suitableway. A slide 13, which carries a drill 14, is slidable along the feedbar 11 by means of two parallel chains 15, a chain 16, and a feed motor17 in the form of a cylinder with a reciprocating piston rod 20. Thefeed motor 17 has two supply conduits 18, 19. If pressure fluid issupplied through the supply conduit 18, the piston rod 20 retracts andthe chain 16 pulls the slide 13 forwards, i.e. downwards in FIG. 1. If,alternatively, pressure fluid is supplied through the supply conduit 19,the slide 13 is pulled backwards, i.e. upwards in FIG. 1, by means ofthe chains 15.

A stationary drill pipe holder or chuck 21 of the vicetype is disposedat the forward portion of the feed bar 11. By means of Bellevillesprings 24, FIG. 3, its jaws 22 are biased to grip a drill string in theform of a drill pipe 23. By the action of pressure fluid upon a piston24a, the force of the springs 24 is overcome and the jaws 22 are forcedto release the drill pipe 23. The pressure fluid is supplied through aconduit 25.

The drill pipe 23 comprises several pipe lengths and a drill bit 26which are joined by screw joints. For rock drilling, the drill bit 26may be a pipe-like diamond drill bit and the first pipe element may be aso called core pipe for collecting a core. A swivel 49 supplies flushwater to the drill pipe.

A chuck 27 with a housing 28 is a part of the drill 14 which in FIG. 5is illustrated in a sectional view. This chuck 27 is rotatablyjournalled in the housing 29 of the drill 14 by means of a rollerbearing 30 and a ball bearing 31. Thus, the chuck 27 is displaced withthe drill 14.

A reversible, pressure fluid actuated rotary motor 32 is arranged torotate the chuck 27 over a gearing which comprises gears 33, 34. Thegear 33 is fixed to the output shaft of the rotary motor 32 by means ofa key 35, and the gear 34 is fixed to the housing 28 of the chuck 27 bymeans of another key 35. The rotary motor 32 has two alternative supplyconduits 36, 37. When pressure fluid is supplied through the conduit 36,the motor 32 rotates forward, and when pressure fluid is suppliedthrough the conduit 37, the motor reverses.

Pressure fluid to the chuck 27 is supplied to .a passage 40 in thehousing 28 of the chuck by means of a conduit 38 and an annular groove39 in the housing 29. Oil is permitted to leak through an annular gap 41between the rotating chuck 27 and the non-rotating housing 29. This oilis collected and conveyed back to a sump 52 by means of a drain conduit42.

In the chuck housing 28, a sleeve-like piston element 43, which hasflanges and is made of an elastomer, is sealingly clamped by means of aspacer sleeve 44 and a cover 45. When pressure fluid is supplied throughthe conduit 38, the piston element 43 forces four jaws 46 of the chuck27 to grip the drill pipe 23. Spring plates 47 are disposed between thejaws 46 to hold the jaws in disengaged position when there is nopressure in the conduit 38. The jaws 46 are guided by guiding pins 48,which transmit torque directly from the housing 28 of the chuck 27 tothe jaws 46 so that the piston element 43 is not subject to torque whenthe chuck is rotated.

In the conduit diagram, FIG. 6, the chucks 21 and 27, the feed motor 17,the rotary motor 32, and the conduits 18, 19, 25, 36, 37, 38, 42 all ofwhich are described above, are represented. The reference numeral 51refers to a pressure fluid supplying unit, which comprises a sump 52 anda pump 53 which is driven by a motor E. Normally, the pressure fluidsupplying unit 51 is situated some distance away from the drillingapparatus. The pump 53 supplies pressure fluid, preferably pressure oil,through a main conduit 54 to a control unit 56 which is indicated bymeans of dashand-dot lines. Preferably the pump 53 is pressurecompensated so that it supplies oil of a constant pressure independentlyof the amount of oil utilized. By means of a return conduit 55, oil isreturned from the control unit 56 to the sump 52.

A manually operated control valve 57 for the rotary motor 32 is suppliedwith pressure fluid from the main conduit 54. This valve 57, which iscalled the rotation control valve, has three alternative positions whichare referred to as positions a, b and c and represented in FIG. 6 by thecorresponding squares a, b,c of the symbol of the valve. With therotation control valve in position b, as illustrated in the figure, theconduits 36, 37 are connected to the return conduit 55, and, thus, therotary motor does not rotate. With the rotation control valve 57 inposition a, the conduit 36 is supplied with pressure oil from the mainconduit 54, and the conduit 37 is drained through the return conduit 55.Therefore, the rotary motor 32 rotates forward. With the valve in theposition 0, the conduit 36 is drained and the conduit 37 is suppliedwith pressure oil so that the rotary motor 32 rotates in reversedirection.

The axial displacement of the drill 14 is controlled by means of amanually operated control valve 58 which is referred to as the feedcontrol valve. This feed control valve 58 has also'three positions whichare referred to as a, b, 0. With the feed control valve 58 in positionb, as illustrated in the figure, the two supply conduits 18, 19 of thefeed motor 17 are connected to theretum conduit 55, and the drill 14does not move axially. If, simultaneously, the rotation control valve 57is in position b, the main conduit 54 is directly connected to thereturn conduit 55 and the entire drilling apparatus is idling. The feedcontrol valve 58 is supplied with pressure oil through a conduit 59independently of the position of the rotation control valve 57. With thefeed con trol valve 58 in position a, pressure oil is supplied to theconduit 18, and the conduit 19 is connected to the return conduit 55.Thus, the drill 14 advances. With the feed control valve 58 in positionc, pressure oil is supplied to the conduit 19, and the conduit 18 isdrained. Therefore, thedrill 14 now retracts.

The supply conduits 25, 38 of the two chucks 21, 27 are branches of acommon supply conduit 60. With a manually operated selector valve 61 ina position a, the supply conduit 18 of the feed motor 17 is connected tothe conduit 60. With the selector valve in a position c, alternatively,the other supply conduit 19 is connected to the conduit 60. With theselector'valve in a position b, the conduit 60 is not connected toeither of the conduits 18, 19. The conduit 38 of the movable chuck 27 isconnected to both of the supply conduits 36, 37 of the rotary motor bymeans of two connection conduits 62, 63. The connection conduits areprovided with valves 64, 75 which permit flow only in the directiontowards the conduit 38. The valve 64 is a simple one-way valve but thevalve 75 is a delaying valve which also acts as a one-way valve. Betweenthe junctions of the connection conduits 62,163 with the conduit 38 andthe junction of the conduits 25 with the conduit 38, a one-wayrestrictor 65 is arranged in the conduit 38. A manually operatedshut-off valve 66 is also arranged in the com duit 38.

The valve 75 will now be described with reference to FIG. 7. It consistsof a slide 76.sliding in a cylinder 77 which .forms part of the conduit63. The cylinder 77 ends in a chamber 78. A bore 79 in the end face 80of the slide 76 is in communication with a transverse bore 81. The slide76 has a head 82 which slides in a cylinder 83 and, as shown in thefigure, it is biased against its end position by means of a spring 84 inthe closed cylinder chamber 85 which is separated by the piston 82. Inthis position, the slide 76 keeps the conduit 63 closed. The motor 32starts rotating backward when its supply conduit 37 is pressurized.Simultaneously the end face 80 of the slide will be loaded by pressureoil and the slide moves therefore to the left in FIG. 7, but since theoil in the cylinder chamber 85 can only escape through a restricted bore86, the piston 82 will dampen the speed of the slide. The motor 32 hastherefore already rotated for instance one revolution before the bore 81reaches the chamber 78 so that the chuck 27 is supplied with pressureoil and grips the drill pipe. In the moment of gripping, the chuck 27transmits to the drill pipe the torque of the motor 32 and the torquewhich emanates from the kinetic energy of the chuck 27, the motor 32,and the gearing. The torque available for breaking a joint can thus bemany times the output torque of the motor 32. As soon as the supply ofpressure oil through either of the conduits 62, 63.stops, the

chuck 27 is relieved of pressure because of its draining through therestriction 65 and through the annular leak space 41.

In the modified form shown in FIG. 8, the restricted bore 86 is replacedby a restricted groove which also is denoted by 86. Since, in thisdesignof the head 82, the head is not provided with any sealing ring, therewill be some leakage also through the clearance space between the headand the cylinder 83. The design shown in FIG. 9 is identical with theone in FIG. 7, but a passage 87 with a one-way valve 88 is arranged topermit the spring 84 to return the slide 76 to the closed end positionin which the slide is shown.

An adjustable pressure reducing valve 67 in the conduit 18 ,sets anupper limit on the feed power. A manometer 68 indicates the feedpressure. Another manometer 69 indicates the pressure in the mainconduit 54. In the conduit 19 of the feed motor 17, an adjustable valveof the relief-valve type is arranged. This valve closes automaticallywhen the pressure in the conduit 19 is lower than a predeterminedpressure. The purposes of this valve 70 are to compensate for the weightof the drill 14 and the drill pipe 23 during drilling and to prevent thedrill with the drill string from moving downwards because of the weightonly. A oneway valve 71 is connected in parallel with the valve 70, andretraction of the drill 14 is permitted. When drilling upwards is to beeffected, the valves 70, 71 are connected in the conduit 18 instead ofthe conduit 19.

For effecting idle run, both the rotation control valve 57 and the feedcontrol valve 58 are set in the neutral positions, i.e. the positions b.The drill pipe 23 is then held by the stationary chuck 21. When drillingis to be started, at first the selector valve 61 is set into position b,then, the rotation control valve 57 is moved into position a. Now,pressure oil flows through the connection conduit 62 to the chucks 21and 27 so that simultaneously, the chuck 27 grips the drill pipe, thechuck 21 releases the drill pipe, and the chuck 27 begins to rotate.Now, when the feed control valve 58 is moved to position a, the drill 14advances. The advance stops automatically when the piston rod 20 of thefeed motor 17 reaches its retracted stop position provided the feedcontrol valve 58 is not shifted before this position is reached.

When the rotation control valve 57 is re-set into the position b, thechucks 21, 27 alternate the engagement tion control valve 57 and thefeedcontrol valve 58 are set in the positions a.

For withdrawing of the drill pipe 23, the selector valve 61 is set inposition 0, and the rotation control valve 57 in position b. The feedcontrol valve 58 is now used as a common control valve for the twochucks 21, 27 and the feed motor 17. When the feed control valve 58 ismoved from position b, the neutral position, to the position c, thechuck 21 releases the drill pipe, but the chuck 27 grips the drill pipeand withdraws it. When the feed control valve 58 is moved into positiona, the chucks alternate engagement automatically, and the drill l4advances without pushing the drill pipe forward. This is repeated, ifnecessary, until the drill pipe is withdrawn an appropriate length.Then, the feed control valve 58 is moved to the position b, the neutralposition, and the rotation control valve 57 is moved to the position 0.Now, the chuck 27 rotates in reverse direction and the supply conduit60, common to the two chucks 21, 27, is drained through the selectorvalve 61 and the feed control valve 58. Through the connection conduit62, however, the movable chuck 27 is sup plied with pressure oil. Onaccount of the restrictor 65, there is oil pressure on this chuck 27,and the chuck 27 grips the drill pipe. The stationary chuck 21,maintains its grip since the flow through the restriction valve isdrained through the common supply conduit 60 of the chucks 21, 27.Therefore, if there is a screw joint of the drill pipe between thechucks, this joint will be broken mechanically when the control valves57, 58 are in these positions. The delaying valve 75 ensures breaking ofvery tight joints as previously described.

When it is desired to reinsert the drill pipe in the drill hole, theselector valve 61 is set in position a. The movable chuck 27 will nowbring the drill pipe 23 forward when the drill 14 advances, and thestationary chuck 21 will hold the drill pipe during retraction of thedrill. With the rotation control valve 57 maintained in the position b,the neutral position, this reinsertion is controlled by means of thefeed control valve 58. When the drill pipe 23 has been introduced so farthat the stationary chuck 21 holds the outer end of the pipe, anotherpipe element is manually screwed on loosely, and the drill 14 isretracted. Then the rotation control valve 57 is moved to the positiona. As a result, the movable chuck 27 engages and rotates the pipeelement, while the stationary chuck 21 holds the drill pipe 23 becauseof the restriction valve 65 which is the case also during breaking ofjoints. Thus, the joint is made. Then, the drill pipe 23 is againinserted so far that the chuck 21 will again hold the outer end of thedrill pipe, and the sequence is repeated.

In order to permit inserting of the drill bit and the first drill-pipeelement through the two chucks 21, 27, the chucks must be opensimultaneously. For this purpose, the operator closes the shut-off valve66, sets the rotation control valve 57 in the position b, the neutralposition, and sets the selector valve 61 and the feed control valve 58in the position a. As result, the drill l4 advances until it stops inits advanced stop position. The two chucks 21, 27 are now open.Alternatively, the selector valve 61 and the feed control valve 58 canbe set in the position 0 so that the drill 14 stops in its retractedstop position. V

In the drilling apparatus described above, the two chucks 21, 27 arethus controlled automatically. During drilling and during making andbreaking of joints, the controlling of the chucks is accomplished bymeans of the control valve 57 of the rotary motor, and, duringintroducing of and withdrawing of the drill string, it is effected bymeans of the control valve 58 of the feed motor.

The chuck 21 may be a power rotated chuck identical with the chuck 27and axially displaceable by another feed motor. The two chucks 21, 27are then rotated with diflerent speed when a joint is to be made orbroken.

Although a joint breaking means in accordance with the invention has aspecial advantage for a rock drill of the kind described, the inventionis not limited to this application but can be varied in many ways withinthe scope of the claims.

What I claim is:

1. Drill string joint breaking means in connection with a rock or earthdrill, comprising a drill string holder and a rotatable chuck in axialalignment for gripping a drill string and breaking a drill string jointbetween the holder and the chuck, said chuck being of the kind which isfluid-actuated and grips when loaded by pressurized hydraulic fluid, ahydraulic motor for rotating the chuck, a fluid supply conduit forsupplying pressurized hydraulic fluid to the motor and including acontrol valve, a branch conduit of said supply conduit connected to saidchuck for supplying pressurized hydraulic fluid to the chuck so as toactuate the chuck, and a delaying valve in said branch conduit adaptedfor delaying the supply of pressurized hydraulic fluid to the chuckuntil the hydraulic motor and thereby the chuck is rotating upon apressurization of the supply conduit of the motor by means of thecontrol valve.

2. Means according to claim 1 in which said delaying valve comprises avalving member which is biased into a closed position but arranged tomove a distance into an open position when acted upon by the pressurizedhydraulic fluid when said supply conduit of the rotation motor ispressurized, and means is arranged to moderate the speed of the valvingmember during this movement to the open position.

3. Means according to claim 2 in which said means for moderating thespeed of the valving member comprises a dashpot.

4. Means according to claim 3 in which said valving member has a headmoving in a dashpot chamber.

5. Means according to claim 4 in which said head is biased by a springtowards said closed position.

6. Means according to claim 5 in which the dashpot has a one-way passageconnected to permit rapid return of the valving member to the closedposition.

7. Means according to claim 6 in which said one-way passage is a passagethrough the head of the valving member.

8. Means according to claim 1 in which said branch conduit is drainedthrough a restricted passage.

9. Means according to claim 1 in which said rotatable chuck is arrangedto be axially displaces along a feed bar by means of a feed motor, andsaid rotation motor is reversible and has an alternative second supplyconduit through which it is supplied with pressurized hydraulic fluidduring making joints and/or during drilling.

10. Means according to claim 9 in which the control valve, when in afirst position, connects the first mentioned supply conduit to a sourceof pressurized hydraulic fluid and said second supply conduit to drainand, when in a second position, connects the first supply conduit todrain and the second to the source of pressure fluid, said control valvehaving also a position in which it isolates both the first and thesecond supply conduits from the source of pressure fluid.

l 1. Means according to claim 10 in which a connection conduit isconnected between said second supply conduit and said branch conduit anda one-way valve is arranged in this connection conduit so as to permitflow only in the direction from the second supply conduit to the chuck.

12. A drilling apparatus for rotary drilling, comprising an elongatedfeed bar, a slide mounted on said feed bar, a feed motor for displacingthe slide along the feed 1 bar, a drill string holder at one end of thefeed bar, a

pressurized hydraulic fluid, a reversible hydraulic motor for rotatingthe chuck, a first fluid supply conduit for supplying pressurizedhydraulic fluid to the motor so as to effect forward rotation of themotor, a second fluid supply conduit for supplying pressurized hydraulicfluid to the motor so as to effect backward rotation of the motor, abranch conduit of said second supply conduit connected to said chuck forsupplying pressurized hydraulic fluid to the chuck so as to actuate thechuck, and a delaying valve in said branch conduit adapted for delayingthe supply of pressurized hydraulic fluid to the chuck until thehydraulic motor and thereby the chuck is rotating upon a suddenpressurization of the supply conduit of the motor.

* III a:

1. Drill string joint breaking means in connection with a rock or earthdrill, comprising a drill string holder and a rotatable chuck in axialalignment for gripping a drill string and breaking a drill string jointbetween the holder and the chuck, said chuck being of the kind which isfluid-actuated and grips when loaded by pressurized hydraulic fluid, ahydraulic motor for rotating the chuck, a fluid supply conduit forsupplying pressurized hydraulic fluid to the motor And including acontrol valve, a branch conduit of said supply conduit connected to saidchuck for supplying pressurized hydraulic fluid to the chuck so as toactuate the chuck, and a delaying valve in said branch conduit adaptedfor delaying the supply of pressurized hydraulic fluid to the chuckuntil the hydraulic motor and thereby the chuck is rotating upon apressurization of the supply conduit of the motor by means of thecontrol valve.
 2. Means according to claim 1 in which said delayingvalve comprises a valving member which is biased into a closed positionbut arranged to move a distance into an open position when acted upon bythe pressurized hydraulic fluid when said supply conduit of the rotationmotor is pressurized, and means is arranged to moderate the speed of thevalving member during this movement to the open position.
 3. Meansaccording to claim 2 in which said means for moderating the speed of thevalving member comprises a dashpot.
 4. Means according to claim 3 inwhich said valving member has a head moving in a dashpot chamber. 5.Means according to claim 4 in which said head is biased by a springtowards said closed position.
 6. Means according to claim 5 in which thedashpot has a one-way passage connected to permit rapid return of thevalving member to the closed position.
 7. Means according to claim 6 inwhich said one-way passage is a passage through the head of the valvingmember.
 8. Means according to claim 1 in which said branch conduit isdrained through a restricted passage.
 9. Means according to claim 1 inwhich said rotatable chuck is arranged to be axially displaces along afeed bar by means of a feed motor, and said rotation motor is reversibleand has an alternative second supply conduit through which it issupplied with pressurized hydraulic fluid during making joints and/orduring drilling.
 10. Means according to claim 9 in which the controlvalve, when in a first position, connects the first mentioned supplyconduit to a source of pressurized hydraulic fluid and said secondsupply conduit to drain and, when in a second position, connects thefirst supply conduit to drain and the second to the source of pressurefluid, said control valve having also a position in which it isolatesboth the first and the second supply conduits from the source ofpressure fluid.
 11. Means according to claim 10 in which a connectionconduit is connected between said second supply conduit and said branchconduit and a one-way valve is arranged in this connection conduit so asto permit flow only in the direction from the second supply conduit tothe chuck.
 12. A drilling apparatus for rotary drilling, comprising anelongated feed bar, a slide mounted on said feed bar, a feed motor fordisplacing the slide along the feed bar, a drill string holder at oneend of the feed bar, a rotatable chuck on said slide, said chuck beingof the kind which is fluid actuated and grips when loaded by pressurizedhydraulic fluid, a reversible hydraulic motor for rotating the chuck, afirst fluid supply conduit for supplying pressurized hydraulic fluid tothe motor so as to effect forward rotation of the motor, a second fluidsupply conduit for supplying pressurized hydraulic fluid to the motor soas to effect backward rotation of the motor, a branch conduit of saidsecond supply conduit connected to said chuck for supplying pressurizedhydraulic fluid to the chuck so as to actuate the chuck, and a delayingvalve in said branch conduit adapted for delaying the supply ofpressurized hydraulic fluid to the chuck until the hydraulic motor andthereby the chuck is rotating upon a sudden pressurization of the supplyconduit of the motor.